The intermediate band solar cell has been proposed as an ultrahigh efficiency source of energy due to the possibility of absorption of two sequential sub-band-gap photons to excite charge from a quantum confined (e.g., quantum dot or well) region into the large band gap barrier region [A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997)]. Unfortunately, high efficiencies using this structure have not yet been realized. Here, we analyze the fundamental limits to power generation in quantum solar cells. When a difference in quasi-Fermi energies between the barrier and the quantum well regions exists due to the presence of photogenerated charge, an upper efficiency limit of 44.5% is achievable due to single photon absorption only. This efficiency is significantly higher than the Shockley-Queisser limit of ∼31% for homojunction cells, but remains below that predicted for two photon excitation (>63%) previously predicted for quantum cells.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)